1. Field of the Invention
This invention relates to a polythiol compound, and an optical material and optical product comprising same. The polythiol compound of this invention is used, e.g. as a useful material for an optical material. The optical material produced from the above polythiol compound, provided by this invention, exhibits a high refractive index and low dispersion or has excellent optical properties, and it is preferred for use in optical products such as a plastic lens, a prism, an optical fiber, a substrate for data reading and storage, a colored filter, an infrared absorbing filter, etc.
Further, it is usable in ornament such as a cup, a flower vase, etc., owing to a high refractive index which the material has as a characteristic.
2. Description of Prior Art
Being light-weighted, unbreakable to a certain degree and easy to dye as compared with glass, plastic has been recently used for an optical purpose, e.g. for producing various lenses. For this reason, polyethylene glycol bisallylcarbonate (CR-39) and polymethyl methacrylate (PMMA) are generally used as a plastic material. Since, however, these plastic materials have a refractive index of not more than 1.50, a lens formed of such a plastic material is required to have a large thickness when the degree is increased. As a result, undesirably, not only the advantage of the light-weight of plastic is lost, but also aesthetic appearance of spectacles of such a material is poor. In particular, when a concave lens is formed of such a material, the peripheral thickness of the lens increases, and birefringence and chromatism undesirably take place. It is therefore desired to develop a plastic material which can take advantage of the properties of plastic having low specific gravity or permit a smaller thickness of a lens, and which has low chromatism, a high refractive index and low dispersion. As a material for such purposes, JP-A-63-46213 discloses a polymer of tetrachloro-m-xhylylenedithiol or 1,3,5-trimercaptobenzene with a diisocyanate compound. JP-A-64-26622 discloses a polymer of pentaerythritoltetrakisthiopropionate with a diisocyanate compound. Further, JP-A-63-309509 discloses a polymer of pentaerythritoltetrakisthiopropionate with a vinyl compound.
However, the thiol compound disclosed in the above JP-A-63-46213 has a low Abbe's number although it has a high refractive index, and a polymer produced therefrom also has defects in that it has a low Abbe's number and poor weatherability. And, the thiol compounds disclosed in JP-A-64-26622 and JP-A-63-309509 have a low refractive index although they have a large Abbe's number, and polymers produced therefrom have defects in that they have a low refractive index and inferior heat resistance.